The present disclosure relates generally to metrology for chemical mechanical polishing, and more particularly to systems and methods for eddy current metrology.
An integrated circuit is typically formed on a substrate by the sequential deposition of conductive, semiconductive or insulative layers on a silicon wafer. One fabrication step involves depositing a filler layer over a non-planar surface, and planarizing the filler layer until the non-planar surface is exposed. For example, a conductive filler layer can be deposited on a patterned insulative layer to fill the trenches or holes in the insulative layer. The filler layer is then polished until the raised pattern of the insulative layer is exposed. After planarization, the portions of the conductive layer remaining between the raised pattern of the insulative layer form vias, plugs and lines that provide conductive paths between thin film circuits on the substrate. In addition, planarization is generally needed to planarize the substrate surface for photolithography.
Chemical mechanical polishing (CMP) is one accepted method of planarization. Conventionally, this planarization method involves holding a substrate on with a carrier head and placing the substrate against a rotating polishing pad. The carrier head provides a controllable load on the substrate to push it against the polishing pad. The polishing pad can be either a xe2x80x9cstandardxe2x80x9d pad or a fixed-abrasive pad. A standard pad has a durable roughened surface, whereas a fixed-abrasive pad has abrasive particles held in a containment media. A polishing solution, including at least one chemically-reactive agent, and abrasive particles if a standard pad is used, is supplied to the surface of the polishing pad (also, some processes use xe2x80x9cabrasivelessxe2x80x9d polishing).
One problem in CMP is determining whether the polishing process is complete, i.e., whether a substrate layer has been planarized to a desired flatness or thickness, or when a desired amount of material has been removed, or whether an underlying layer has been exposed. Overpolishing (removing too much) of a conductive layer or film leads to increased circuit resistance. On the other hand, underpolishing (removing too little) of a conductive layer leads to electrical shorting. Variations in the initial thickness of the substrate layer, the slurry composition, the polishing pad condition, the relative speed between the polishing pad and the substrate, and the load on the substrate can cause variations in the material removal rate. These variations cause variations in the time needed to reach the polishing endpoint. Therefore, the polishing endpoint cannot be determined merely as a function of polishing time.
Two techniques are used to compensate for variations in the polishing endpoint. In-line metrology systems measure the thickness of layers on the substrate before and after processing. Assuming the layer thickness is determined prior to polishing, the polishing time can be adjusted to provide more accurate control of the amount of material remaining on the substrate after polishing. In-situ systems monitor the substrate during polishing to measure the amount of material removed or to detect sudden changes in substrate characteristics that indicate that a layer has been exposed.
A recent in-situ endpoint detection technique induces an eddy current in a metal layer on the substrate and uses an eddy current sensor to monitor the change in the eddy current as the metal layer is removed.
An in-line eddy current monitoring system generates a signal related to the thickness of a conductive region such as a conductive layer on a wafer. The in-line eddy current monitoring system may be used either prior to or subsequent to polishing the wafer using a chemical mechanical polishing system.
In general, in one aspect, the invention is directed to a system that includes a polishing apparatus having one or more polishing stations for polishing of a substrate, a substrate transfer system to transfer a substrate to and from the polishing stations, a substrate holder accessible by the substrate transfer system to hold the substrate at a location away from the polishing stations, an eddy current monitoring system having a probe positionable proximate to the substrate in the substrate holder to induce eddy currents in a conductive region of the substrate and generate a signal associated with a thickness of the conductive region, and a controller to receive the signal from the probe. The polishing stations operate with a plurality of polishing parameters, and the controller controls at least one of the plurality of polishing parameters in response to the signal.
Implementations of the invention may include one or more of the following features. The substrate transfer system may include a wet robot, and the substrate holder may be located along a path of the wet robot. The system may include a factory interface module with at least one port to receive the substrate from a cassette, and the substrate holder may be located in the factory interface module. The transfer mechanism may include a factory interface robot to transfer the substrate to and from the factory interface module. The eddy current monitoring system may include a translation mechanism to move the probe across a surface of the substrate, e.g., along a diameter of the substrate. The translation mechanism may include a rotation mechanism to rotate the substrate with respect to the probe. The translation mechanism may include a first translation to move the probe along a first direction across the surface of the substrate and a second mechanism to move the probe along a second direction different from the first direction. The system may include a cleaner, and the substrate holder may be located in the cleaner. The substrate holder may be located in the polishing apparatus. The system may include another substrate holder to hold the substrate at another location away from the polishing stations, another probe positionable proximate to the substrate in the another substrate holder to induce eddy currents in a conductive region of the substrate and generate another signal associated with a thickness of the conductive region, and the controller may control at least one polishing parameter of the chemical mechanical polisher based on the another signal from the another probe. The controller may be configured to cause the substrate transfer system to place the substrate in the substrate holder prior to or after placing the substrate in the polishing station.
In another aspect, the invention is directed to a system that includes a cleaner to receive polished substrates from a polishing apparatus and an eddy current monitoring system. The cleaner has a substrate holder, and the eddy current monitoring system has a probe positionable proximate to the substrate in the substrate holder to induce eddy currents in a conductive region of the substrate and generate signals associated with a thickness of the conductive region.
In another aspect, the invention is directed to a system that includes a factory interface module to receive substrates and an eddy current monitoring system. The factory interface module has a substrate holder, and the eddy current monitoring system has a probe positionable proximate to the substrate in the substrate holder to induce eddy currents in a conductive region of the substrate and generate signals associated with a thickness of the conductive region.
Implementations of the above inventions may include one or more of the following features. The system may include a controller to modify at least one polishing parameter of the polishing apparatus based on the signal from the probe.
In another aspect, the invention is directed to a chemical mechanical polishing system that has one or more carrier heads for holding a substrate during polishing, one or more polishing stations, a substrate holding station separate from the polishing stations, and an eddy current monitoring system having a probe, the probe to be positioned proximate to the substrate in the substrate holding station to induce eddy currents in a conductive region of the substrate and generate signals associated with a thickness of the conductive region.
Implementations of the above inventions may include one or more of the following features. The system may include a controller to modify at least one polishing parameter of the polishing apparatus based on the signal from the probe.
In another aspect, the invention is directed to a system that includes a measuring station to hold a substrate, an eddy current metrology system, and a controller. The measuring station is positioned at a location away from a polishing pad of a chemical mechanical polishing apparatus. The eddy current metrology system has a probe to be placed in proximity to a conductive region of the substrate at the measuring station, a driver unit to excite the probe, and a sensor unit to generate an output signal associated with a thickness of the conductive region. The controller is configured to adjust one or more polishing endpoint criteria based on the output signal from the eddy current metrology system.
Implementations of the above inventions may include one or more of the following features. The location may be chosen from the group consisting of in the chemical mechanical polishing apparatus, in a substrate transfer system, in a cleaner, and in a factory interface module.
In another aspect, the invention is directed to a method in which a substrate is transported with a substrate transferring system to a measuring station located separate from a polishing station of a polishing apparatus, a probe of an eddy current system is positioned in proximity to the substrate at the measuring station, the probe is excited to induce eddy currents in a conductive region of the substrate, measurement signals are generated with the eddy current system associated with a thickness of the conductive region, and a polishing parameter of the polishing apparatus is controlled based on the signals from the eddy current system.
Implementations of the above inventions may include one or more of the following features. The substrate may be polished. The polishing step may occur prior to the transporting step so that the polishing parameter controls polishing of a subsequent substrate, or the polishing step may occur after the transporting step so that the polishing parameter controls polishing of the substrate.
In another aspect, the invention is directed to an article comprising a machine-readable medium storing instructions operable to cause one or more machines to perform the above methods.
The details of one or more implementations of the invention are set forth in the accompanying drawings and the description below. Other features and advantages of the invention will be apparent from the description and drawings, and from the claims.